From what I've gathered after years of speculation and confusion surrounding the INTENDED use of these carriers, both the front (where it mounts to the rest of the carrier) and back (where the back-bar mounts) of the U-shaped shoulder pieces should be even with each other. This leaves a symmetrical shoulder piece that allows the player's shoulders to sit as far up in the carrier as possible, not to mention that the carrier will no longer rest incorrectly on the player, assuming that they are practicing good posture.
If this doesn't achieve a comfortable position for the player, I'd recommend getting two strong guys to bend the should pieces to better fit a smaller person's frame. I find myself doing this to my own carriers, having a slender build myself.
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Zach Harston
harston.zach @ yahoo.com
(281) 723-3580
OASAASLLS